Hybrid ring coupling arrangement



April 46, 1957 H. T. BUDENBO-M HYBRID RING COUPLING ARRANGEMENT OriginalFiied Oct. 5, 1948 4 Sheets-Sheet l OUTPUT NULL BALANCE (CONJUGACV) dbFREQUENCY A T TORA/EV April 16, 1957 H. T. BUDENBOM 2, 8

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lNl/ENTOR B 7. BUDENBOM United States Patent HYBRID RING COUPLINGARRANGEMENT Horace T. Budenbom, Short Hills, N. J., assignor to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York Original application October 5, 1948, Serial No. 52,856.Divided and this application March 19, 1952, Serial No. 277,496

3 Claims. (Cl. 333-11) This invention relates to wave transmissionsystems and particularly to wave balancing and power dividingarrangements for use in such systems.

This is a division of my copending patent application Serial No. 52,856,filed October 5, 1948.

In radio and other high frequency signaling and control systems, it isoften desirable to distribute high frequency wave power supplied from asingle source between a plurality of receiving channels or loads whilemaintaining a high degree of isolation or conjugacy between theindividual channels or loads so as to prevent interfering effects. Anumber of different types of coupling networks for this purpose havingbridge or null balance characteristics analogous to those of the hybridcoil commonly used in voice frequency communication practice, which areparticularly adapted for use in ultra-high frequency systems, aredisclosed in the United States Patent Number 2,445,895, issued July 27,1948, and are further described in the article Hybrid Circuits forMicrowaves by W. A. Tyrell, published in the November 1947 issue of theProceedings of the Institute of Radio Engineers. One described type ofstructure for this purpose, referred to as a hybrid ring, comprises asection of dielectric wave guide, coaxial cable, or other type oftransmission line, formed into a closed transmission loop or ring andodd number of half-wavelengths in mean perimeter and four series orshunt branching connections or taps to the loop at appropriately spacedpoints. In one form of hybrid ring described, the four branch taps areconnected in series electrically with the loop (which for a waveguidering is a connection in the electric plane), and the electrical spacingsbetween the branch taps are selected so as to provide two paths aroundthe loop between each two (non-adjacent) branch taps differing inefiective elec trical length by a half-wavelength at the designfrequency. If electromagnetic waves of that frequency are applied to theloop through any one of the four branch taps, the two portions thereoftransmitted overthe two sides of the loop in opposite directions will beof opposite phase at the point of connection of the oppositely situatedbranch tap, which results in a voltage maximum (or current minimum) atthat point, and will be of the same phase at the points of connection ofthe two intermediate branch taps to the loop, which results in a voltageminimum (or current maximum) at these point due to the fact that theeffective electrical length of the two paths traversed by the two waveportions in reaching the latter points are either equal or differ by anintegral number of wavelengths. Because of the series connections, thebranch tap connected at the voltage maximum point will receivesubstantially no power, whereas the two intermediate branch taps atvoltage minimum points will each receive part of the wave power appliedto the loop and, if each of the taps is terminated in its characteristicimpedance, each of the taps at a voltage minimum point will receive halfthe input power.

One known use of this type of hybrid ring is to provide 2,789,271Patented Apr. 16, 1957 ice as outputs from two (non-adjacent) branchtaps, the sum and difference, respectively, of two input voltages of thesame frequency respectively applied to the loop through a different pairof branch taps. For the case of sum and difference action, the hybridring has an advantage when the power level is high over the waveguidehybrid junction (particular orthogonal junction of four rectangular waveguides), also disclosed in the aforementioned Tyrrell patent, since ithas been found considerably less susceptible to voltage breakdown. Forpower division the hybrid ring has the advantage of higher powercapability and, for some applications, of greater simplicity.

One object of the invention is to adapt a hybrid ring of theabove-described general type for dividing wave power supplied theretofrom a single source between a greater number, more than two, ofreceiving channels or loads, while maintaining a high degree ofisolation (conjugacy) between some or all of the individual channels orloads. This is accomplished in accordance with one embodiment of theinvention by increasing the number of series branch taps to the loop tofive or more with electrical spacings between them such as to provide agood null balance between each branch tap and one or more of the otherbranch taps, connecting the source of wave power to one of the branchtaps, iteratively terminating the branch tap or taps which are balancedwith respect to said one tap, and connecting each of the receivingchannels'or loads to a different one of the branch taps which areunbalanced with respect to the branch tap to which the source of wavepower is connected.

Another object is to increase the frequency range or band over which auseful balance or conjugacy may be obtained between two or more lines orcircuits in a wave transmission network by the use of hybrid ringstructures. This is accomplished by connecting a hybrid ring having agiven number of branch taps or arms in tandem with two or more hybridrings having a greater number of branch arms or taps in such manner asto nearly add logarithmically the attenuations obtainable betweenconjugate taps or arms of the several hybrid ring structures. In oneembodiment of this species of the invention, the coupling arrangementbetween the source of power and the receiving channels or loads betweenwhich the power is to be divided with conjugacy between them comprises afour-arm hybrid ring in tandem with one, two or more five-arm hybridrings. A feature of the invention is a power dividing device comprisinga concentric arrangement 'of a four-arm hybrid ring and a five-armhybrid ring coupled in tandem, the mean perimeter of the outer five-armhybrid ring being expanded in an odd integral ratio with respect to themean perimeter of the inner four-arm hybn'd ring so as to enablestraight cross-connections to be made between the arms of the twotandemconnected rings.

Another object is to enable the multiple operation of a number ofmagnetrons or other transmitters operating in the microwave frequencyregion, i. e., to sum their output powers in a single line or circuit.

Another object is to produce division of the high level output of asingle magnetron orother microwave transmitting device into a number ofparts and to dissipate the power of these parts in separate loadterminations of reasonable design.

The various objects and features of the invention will be betterunderstood from the following detailed description when read inconjunction with the accompanying drawings in which:

Figs. 1 and 1A, respectively, show a perspective anda cross-sectionalview of a four-arm wave-guide hybrid ring known in the prior art; A

Figs. 2 and 2A show diagrammatically the application of a four-armhybrid ring structure of the type' illustrated in Figs. 1 and 1A forpower division in a radio system, and a curve showing how the nullbalance in this structure is affected by changes in frequency,respectively;

Figs. 3-, 4 and 5 show diagrammatically a five-arm, a SlX- rm and atenarm hybrid ring, respectively, embodyiiig the invention used forobtaining power division with conjugacy;

Figs. 6, 7 and 8 show diagrammatically null balance arrangements inaccordance with the invention employing two or more hybrid rings intandem, and Figs. 6A, 7A and SA Show curves comparing the performance ofthese hybrid ring structures with that of a single hybrid ring'and'other t-andem structures;

Fig; 12 shows diagrammatically a rn'ul'ti-tap hybrid ring structure inaccordance with the invention employing a different spacing between tapsthan those of Figs. 3 to 8;

Figs. 9 to ll, inclusive, 12A and 13 illustrate diagrammaticallyapplications of the hybrid ring arrange ments of the invention shown inFigs. 3 to 8, inclusive, and 12 for providing power division andsummation in various radio and ultra-high frequency radio systems;

Fig. 9A shows curves illustrating the operation of a hybrid ring powerdividing arrangement in accordance with the invention in the radarsystem of Figure 9; and

Figs. 14A, 14B and 14C show diagrammatically how a multi-tap hybrid ringarrangement having all series type connection of the taps to the ring isconverted to a hybrid ring arrangement employing both series and shunttype connections of the taps to the ring.

Reference will first be made to Figs. 1 and 1A showing one specificembodiment of the general type of hybrid ring structure to which theinvention applies. In this embodiment, as shown, the hybrid ringcomprises a section of hollow pipe wave guide of rectangular crosssection, formed'into a continuous ring or annulus R one andone-halfwavelengths x in mean circumference with four Wave guide connections. 1,2, 3 and 4 thereto, connected as branches symmetrically to thewave-guide ring R at the point A,B, C and D, respectiveiy, in theelectric or E-plane which corresponds to a series electrical connection.'The wave-guide branches 1 to 4 may be of the'usual variety comprisinghollow pipe of rectangular cross section in which the electric orE-plane transverse dimension is about half the other (magnetic orH-plane) transverse dimension. Also, the height of the ring or annulus Rin this particular embodiment may be equal to the H-plane dimension ofthe wave guide and its width such as to provide an impedance match(onthe /2 basis as taught in the aforementioned Tyrrell patent). Thering and branches of the general type of hybrid ring structure to whichthe invention is applicable may com prise. other types of wave guideconstruction, coaxials or wires, and loop shapes other than circularmaybe used. Also, the connections of the several branches to the ring orannulus may be in the magentic or H-plane, equivalent to a shunt orparallel electrical connection, as also taught in the aforementionedTyrrell patent.

As indicated in Fig. 1A, the effective electrical lengths of the pathsaround the ring between the branch arm 2 and the branch arm 3, betweenthe branch arm 3 and the arm 4, and between the branch arm 4 and thebranch arm 1 are each equal to a quarter-wavelength; and the efiectiveelectrical length of the path around the ring between the branch arm 1and the branch arm 2 is three quarter-wavelengths. These spacingsprovide two electrical paths around'the ring between each branch arm andthe oppositely situated (non-adjacent) branch arms differing inelectrical length by a half-wavelength. If a wave input E1 is applied tothe wave guide ring R through the branch arm 1 and a second input waveE2 of the same frequency is applied to the ring through branch arms, thesum of the two input powei's, Ei+E- will appear as an output in thebranch arm 4 since the path lengths from each input to the outputbetweenthem are equal; and the difference of the two input powers, Ei-Ez, willappear as an output in the branch arm 2 since the path lengths from eachinput to the remaining output differ by one-half wavelength. With properdesign and terminations for the branch arms, the four-arm hybrid ringstructure shown exhibits these additional properties; the branch arms 1and 3 are conjugate (a high transmission. loss obtains between them);the s uin and difference branch arms 4 and 2 are conjugate; a singleinput to the ring through branch arm 4 will divide equally, half theinput power appearing in branch arrn 1 and half in branch arm" 3; asingle input to the ring through branch arm 2 will divide equally, half"the" input power appearing. in branch arm 1 and half in branch arm 3;and a single input to the ring through branch arm 1 or 3 will be dividedequally between the branch arms 4 and 2'. However, if the branch arm 2were removed, the power input through branch arm 4 would still dividebetween branch arms 1 and 3, but the branch arms 1" and 3 will no longerremaih' conjugate.

Fig. 2 shows a four-arm wav'e-guide hybrid ring of the type of Figs. 1'and lA used to provide two way power division with conjugacy in a radiosystem between a pair of horn antennas A1 and A2 respectivelyconnectedto the branch arms 4- and 2. If input power is applied to thering through one branch arm, say arm 1, and the opposite branch arm 3 isproperly terminated, the output power will be divided between the brancharms 4 and 2 leading to the antennas A1 and A2, respectively, but thebalanc'e be'tween the two pairs of oppositely sitt'rated branch armswill be frequency sensitive. As shown, by the curve of Fig. 2A, the nullbalance (conjugacy) is quite good in the immediate vicinity of the cle'sign center frequency where-the mean perimeter of the-ring is hear oneand one-half wavelengths in theguide.- On either side ofthe-peak',-however,' as shown, the null balance depreciates, in aman'n'er similar to that of the response of a resonant circuit forapplied frequencies on either'side of. the resonant frequency. While thebalance of interest is that of 3 with respect to the two antenna brancharms 2 and 4, it isequivalent to measure the balance between the arms 1and 3, which is the usual laboratory procedure.

Fig. 3 shows the use of a five-arm 1- /2) waveguide hybrid ring. withseries connections of the arms to the closed loop or ring in accordancewith the invention as a three-way power divider. The electricalspacingaround the ring between branch arms 1 and 2, between branch arms2 and 3, between branch arms 3' and 4, and between arms 4 and 5 isMrxeaeh, and that between branch arms 1 and 5 is /z-A. With an inputapplied to arm 2 and arm 4 iteratively terminated as showndiagrammatically, the output of branch arm 3 will be effectivelyisolated (conjugate) fromthe output atarms 1 and 5-, but arms 1 andSwill not be isolated. For one experimental sample, the relative levelsat the three outputs were measured to be as follows, relative to theinput level; at branches 1 and 5, 8 decibels each as compared to- 5'decibels at output 3.

Fig. 4 shows the use of a six-arm 1 /2 wave-guide hybridring with seriesconnections of the arms" to the ring in accordance with the invention asa= threeway power divider. An electrical spacing of /4/\ is used betweeneach two'adjacen't arms of the six arms. With a wave input applied tothe ring through branch arm 1 and with branch arms- 3 and 5 iterativelyterminated, wave outputs will appear atbranch arms 2;'.4and- 6 and allofthese are isolated with respect to each other. In a measured sample, thelevels at the three output points relative to that at branch arm 1 were:at branch arms 2 and 6', 4.5 decibels each as compared to about 8.5decibels at branch arm 4. v v

Fig. 5 shows a ten-arm 2 /zX wave-guide hybrid ring or the five-armhybrid ring used alone.

with series connections of the arms to the ring in accordance with theinvention adapted for providing power division between five loads with ahigh degree of isolation between them. As indicated, each two adjacentbranch arms of the wave guide hybrid ring are electrically spaced fromeach other by AA. With wave power applied to the ring through branch arm1, and with the alternate branch arms 3, 5, 7 and 9 iterativelyterminated, the output wave power will be divided between the fivebranching arms 2, 4, 6, 8 and with a high degree of isolation betweenthe individual output branches. One experimental sample of such astructure showed the following output levels compared to an input levelof one decibel at branch 1: at branch arms 2 and 10, 5.4 decibels; atbranch arms 4 and 8, 11.6 decibels; and at branch arm 6, 14.4 decibels.

Obviously, the power dividing arrangements of Figs. 3 to 5 are notlimited to hybrid rings of 1 /2 in mean perimeter, but may be expandedin the manner taught by Tyrrell in the aforementioned I. R. E. articleof November 1947 without altering any of the circuit characteristics, bythe application of either or both of the following rules:

(a) An integral number of wavelengths may be added to or subtracted fromany arc (portion of ring between center lines of adjacent branch arms);

(b) A pair of half-wavelengths may be added to or subtracted from anytwo arcs.

The frequency band over which a useful balance (of the order of 35-40decibels minimum) may be obtained with hybrid rings can be broadened inaccordance with the invention by the use of the structure shown in Fig.6. This structure comprises a pair of 1 /2.\ wave guide hybrid rings R1and R2 connected in tandem. The lower ring R1 may be identical with thefour-arm hybrid ring of Fig. 2, and the upper ring R2 identical with thefivearm hybrid ring of Fig. 3, the electrical spacings between thesimilarly numbered branch arms of the two rings being the same as shownin Figs. 2 and 3, respectively. The two branch arms 5 and 1 of the upperfivearm ring R2 separated by a half-wavelength are connected directly tothe two branch arms 4 and 2, respectively, of the lower four-arm ringalso separated by a half-wavelength as shown. The branch arms 2 and 4 ofthe upper five-arm ring R2 are connected to the horntype antennas A2 andA1, respectively. The branch arm 3 of the lower four-arm ring R1 isterminated iteratively.

When the conjugacy between the branch arm 3 of the upper ring and thebranch arm 1 of the tandem arrangement of Fig. 6 is measured, it isfound to be much improved over that obtainable with a four-arm hybridring The resulting null balance-frequency characteristic for thetandem-ring arrangement of Fig. 6 is shown by the solid-line curves ofFig. 6A, with the corresponding characteristic for the four-arm hybridring R1 of Fig. 3 shown by the dotted curve for comparison. The reasonfor the improvement may be discussed in terms of conjugacy for a singlewave input to the arrangement of Fig. 6 at the branch arm 3 of the upperring. At the design frequency, the outputs 5 and 1 of the upper five-armring are conjugate with respect to such an input. As the frequency isshifted .from the design center, the voltages which will begin to appearin the branch arms 5 and 1 of the five-arm ring are oppositely phaseddue to the half-wave separation between these branches. The outputs ofthe two branch arms 5 and 1 of the five-arm ring are supplied to thefour-arm ring through branch arms 4 and 2 of the latter ring and arecombined therein in difierential fashion so as to provide a sort offirst order cancellation of frequency sensitivity of the conjugacy, thuseffecorder of 35 to 40 decibels or better was attained over a frequencyrange from 3.13 to 3.53 centimeters wavelength. In the particulararrangement built and tested, the cross section of the rectangular waveguide used was .900 x .400 inch, inside measurement. The rings weremachined brass blocks. Each block was split in a plane perpendicular tothe ring axis at the mid-point of the broad guide dimension.

The tandem arrangement of Fig. 6 is not limited to the particular ringdimensions shown, 1 /2). mean perimeter, for each ring, but thedimensions of each ring may be expanded in the manner taught by Tyrrellin the aforementioned I. R. E. article by the appropriate addition ofhalf or full wavelength sections.

Fig. 7 shows a modified tandem arrangement of a four-arm and a five-armhybrid ring in which the perimeter of the five-arm ring is expanded inan odd integral manner (as 3, 5, 7, 9 X 1 /27\) such that the fourarmring may be built internal to the five-arm ring and thus enable straightcross-connections to be made between the connecting arms of the tworings. The conjugacy obtained by this concentric hybrid ring structureloses somewhat in band width with the larger perimeter, the band widthover which conjugacy will be attained being intermediate between thatobtainable for the hybrid ring structures of Figs. 2 and 6, as indicatedby the relative performance curves of Fig. 7A.

It appears that, subject to practical leakage limitations, the degree ofconjugacy can be increased indefinitely by the addition of other hybridrings to the tandem structure. Fig. 8 shows the tandem combination of afour-arm hybrid ring R1 and two five-arm hybrid rings R2 and R3 eachhaving a mean perimeter of 1 /2) Two of the branch arms of the centralfive-arm hybrid ring R3 which are separated by a half-wavelength areconnected to two of the branch arms also separated by a half-wavelengthof the end five-arm ring R2, and the other two branch arms of thecentral five-arm ring separated by a half-wavelength are connected tothe two branch arms 4 and 2 of the four-arm ring R1 separated by ahalf-wavelength. The remaining arm of the central five-arm hybrid ringR3 and the arm 3 of the four-arm ring R1 are terminated iteratively. Asshown by the conjugacy curves of Fig. 8A, the performance of the tandemhybrid ring structure of Fig. 8 (see solid line curves) relative to thehybrid ring structures of Figs. 2 and 6 (see dotted curves) as regardsthe frequency band over which conjugacy is obtained has been furtherimproved. If a plot of conjugacy in decibels is made against thelogarithm of the percent departure of frequency from the design center,it will be found that over a considerable percentage interval, theslopes of the conjugacy characteristics are nearly as follows: onehybrid ring-6 'decibels per octave; two hybrid rings12 decibels peroctave; and three hybrid rings-- 18 decibels per octave. In thestructures of Figs. 6, 7 and 8, it was found that the addition of hybridrings in tandem did not affect materially at the design center frequencyeither the division of power between branch arms 2 and 4- for an inputat branch arm 3 in the five-arm hybrid ring R2 or the degree ofconjugacy between branch arms 2 and 4. The individual rings of thetandem ring structures may be expanded in perimeter in the manner taughtby the aforementioned Tyrrell patent.

For the case of the five-arm 1 /21 hybrid ring structure of Fig. 3, alloutput levels could be nearly equalized, and one extra isolated outletgained, by connecting a four-aim hybrid ring such as shown in Figs. 1and 1A or Fig. 2 to arm 3. For the six-arm 1 /21 hybrid ring of Fig. 4,two added isolated outputs could be obtained, and all outputs nearlyequalized, by connecting a four-arm hybrid ring to each of the arms 2and 6.

The hybrid ring arrangements of the invention are particularlyapplicable for providing the desired division of power with conjugacy inradar systems in which it is desired to measure accurately the sum anddifference of two input voltages. An example of this is a monopulsesystem for angle tracking of moving targets in which complete (two)directional determinations of the arrival angle of the radar wave isobtained within the period of one individual echo pulse by adifferential amplitude method. The component elements of'such a systemand their initial operationfor one angle coordinate are illustrated inFigs. 9 and 9A. As shown in Fig. 9, in such a structure .a pair of hornantennas and 29 are arranged to feed a lens antenna 60, and theelectrical signals (echoes) E1 and E2, respectively received by theantennas 1t and are fed to a power dividing arrangement which may be ahybrid ring structure in accordance with the invention, such as isillustrated in Figs. 3, 6, 7 or 8, which is capable of producing thesum, E1+Ez, of these two input voltages at one output terminal and theirdiiierence, E1E2, at another output terminal 5%). The antenna-powerdividing arrangement assembly is arranged to be traversed (rotated) sothat the antenna scans a region in which a target 79 is moving. Forpresent purposes, the target 70 may be assumed to be an active source(as in beacon tracking), although in other radar applications the targetwill be passive; in the latter case, during the period of a transmittedpulse the target 70 is illuminated by high level transmitter powerapplied at terminal 40 of the power dividing network 36 and divided bythat network into two portions which areradiated by the horn antennas 10and 2! respectively. When the antenna assembiy traverses to a positionalong the indicated axis line 80, equal voltages will be induced intothe horn antennas 10 and 253 by the wave energy arriving from the target7d and focussed by the lens 60; in this event,-no energy will appear atthe output terminal of the hybrid structure 30, assuming the hybrid andassociated wave guide structures to be perfect. As soon, however, as theassembly traverses off the axis of symmetry 80, the voltages E1 and E2will cease to be equal, one or the other predominating in amplitudeaccording to the direction of traverse. Accordingly, a difierencecomponent, E1-E2, will appear at the terminal 50.

The behavior of the radio frequency voltages as the antenna assemblytraverses is indicated by the curves of Fig. 9A. The slope of thedifference (Er-E2) curve is actually quite steep and is approximatelylinear in the cross-over region (traverse angle=0).

Conditions often arise in radar design where it is advantageous tosupply microwave power to several loads. in certain of these cases, itis also necessary that the loads remain mutually conjugate. As anexample of the latter case, there is the problem of beating oscillatorsupply to the several channels of a monopnlse tracking system theoperation of which'for one angle coordinate has already been describedin connection with Figs. 9 and 9A. Operation in both angle coordinatesrequires a common beating oscillator supply to a sum channel such as hasalready been referred to in connection with Figs. 9 and 9A and, inaddition, two error signal channels, i. e., an azimuth error signal andan elevation error signal channel. All three channels must be mutuallyconjugate to prevent interchannel cross-talk via the beating oscillator.

Fig. 10 illustrates diagrammatically how a hybrid ring arrangement inaccordance with the invention could be utilized for the latter purpose.The lens-feed hornpower divider (hybrid ring) assembly is genericallydenoted by the box 1% in the figure, from which extend three channeloutputs 2th), 360 and 490 for the error 1,

:such a system, other drains on the beating oscillator may 8 aresuitable for use in such a system for providing the high degree ofconjugacy over the desired frequency band required between the three ormore receiving channels in such a system.

Anothenapplication for the hybrid ring arrangementsin accordance withthe invention is to terminations for high power radar transmitters asillustrated diagrammatically in Fig. 11. In such cases, while conjugacymay not be requisite, the use of power division may be most advantageousto prevent overheating of the wave-guide terminations (iterative).Furthermore, the use of the hybrid ring structures of the invention forsuch division may be desirable owing to their superior power handlingcapabiiities. in the arrangement of Fig. 11, the numeral 1 designates atransmitter, such as a magnetron, 2 a power divider for dividing thepower from the transmitter into the required number of wave portions,and 3, 4' n separate load terminations.

Fig. 12 illustrates a multi-tap hybrid ring structure in accordance withthe invention having a spacing of it) between taps around the ring,where is the wavelength in the guide and n is an integer, which issuitable for use in providing multiple operation of a number ofmicrowave transmitters in the manner illustrated in Fig; 12A. For mtransmitters, m-j-l taps are provided, the extra tap 0 being used for apower outlet. Since a ring of iength 12A can be shown, neglectingdissipation, to be equivalent to a strap, the net etfect is that the mmicrowave transmitters T1, T2 Tm respectively connected to a differentone of the m taps, l, 2 m, are simply tied in series, and the sum of theoutput powers of all of these transmitters may be taken off from theremaining tap 0. When used in the reverse manner, as diagrammaticallyillustrated in Fig. l, where the hybrid ring structure of Fig. 12 isemployed as the power divider 2, a single microwave transmitter 1'supplies its output power to the ring through one of the n+1 taps andthe divided power is distributed between separate terminations 3', 4 nrespectively connected to a different one of the it other taps. In suchfashion, the heating requirements laid on the various absorbers arereduced.

A further application of power division by the hybrid ring arrangementsof the invention is in connection with the design of antenna feedshaving specified power distribution. Thus, an antenna aperture feduniformly across its dimension has good gain but excessive side lobes,whereas the side lobes can be very markedly reduced, with only minorgain reduction, by tapering the feed to 10 decibels down or more at theedges of the aperture. Again, special feed distributions are useful inachieving the well-known cosecant squared type of pattern. From thedescription given above, it should be clear that combinations of thepower dividing hybrid structures in accordance with the inventionshould'enable division of the high power supplied by a transmitter, suchas a magnetron or other transmitting oscillator, into a feed horn arrayso that the illumination of the antenna aperture will vary in almost anydesired manner. Fig. 13 illustrates this general application. 7 It isdesired, in order to reduce side lobes, to taper the illumination of thelens L at the edges. Accordingly, the power of the transmitter T isdivided by a hybrid ring array in accordance with invention comprisingthe tandem corinectedhybrid rings R4, R5 and R6, illustrateddiagrammatically, each power outlet of which terminates in one'of thesmall horn antennas A. In the illustration, which is no way intended tobe restricted to any particular details of the component elements, thepower of transmitter T is split three ways in the six-arm l /27\ hybridring R4, two'arrns of which are terminated iteratively asshown. Oneoutlet from hybrid ring R4 carrying the least power supplies the centralone of the feed horn antennas A directly. The two other power outlets ofhybrid ring R4 respectively feed into one arm of one of the ten-arm 2/zk power divider hybrid rings R5 and R6 in accordance with theinvention. The two outlets of least power from rings R5 and R6 feed thehorns A illuminating the edges of the lens L. The two power outlets ofnext higher power level from each of the rings R5 and R6 feed certain ofthe horn antennas A nearer the center of the lens L, and those outletsof highest power level from each ring R5 and R6 feed certain of the hornantennas A still nearer the central portion of the lens L. Thus atapered illumination is built up.

As stated previously, the invention is not limited to the use of air orother dielectric Wave guide in the ring and branching arms of the hybridstructures illustrated and described, as coaxial cable, parallel wirelines or other types of lines, or combinations of wave guide and othertypes of lines may be employed. Also, shunt connections of the branchesto the ring or loop may be employed in place of the series connections.The design of such structure employing shunt connections to accomplishthe above-mentioned objects of the invention will be obvious to personsskilled in the art by application of the above-mentioned two rules takenfrom the aforementioned Tyrrell article and the additional rule recitedtherein: If a series element of impedance Z on a transmission line ofcharacteristic impedance K0 is replaced by a shunt element of impedanceKo /Z, on one side of which is added a quarter-wavelength of line and onthe other side a three-quarter wavelength of line, the entireperformance of the circuit is unaltered.

Figs. 14A, 14B and 14C show diagrammatically specific illustrations ofthe conversion of an all series type hybrid ring in accordance with theinvention to a hybrid ring employing both series and shunt connectionsof the taps to the ring. Fig. 14A illustrates diagrammatically a sixarml /zk hybrid ring, similar to that shown in Fig 4, employing seriesconnections of all six arms.- In Fig. 14B the Tyrrell rule last quotedabove has been applied to produce :a six-arm 3 /zk hybrid ring in whichtwo of the output arms 01 and 02 are joined to the ring by shuntconnections and the other four arms by series connections, and in Fig.14C the first-mentioned two Tyrrell rules have been applied to reducethe mean perimeter from the three and one-half wavelengths of Fig. 148to two and one-half wavelengths while maintaining the twoshunt-connected arms and the four series-connected arms. The shuntconnections of certain of the arms or taps to the ring in the hybridring arrangements of Figs.

14B and have been indicated diagrammatically in these figures by a dotat the point of connection. The connections of the other arms or taps tothe ring in these figures not having a dot at the point of connectionare series connections. The wavelength spacings required in each caseare shown on the three figures.

Other modifications of the five :or more arm hybrid ring structures .andtandem hybrid ring structures illustrated and described which are withinthe spirit and scope of the invention will occur to persons sldlled inthe art.

What is claimed is:

1. A microwave coupling device consisting of a hybrid wave-guide ringand at least three branch taps at spaced points around the ring with anelectrical spacing of n) between each two successive taps around thering, where A is the wavelength in the guide and n is an integer.

2. A device for dividing the high level output power of a singlemicrowave source into In parts and for distributing the divided wavepower between a corresponding number of load terminations, comprising aclosed transmission loop made from wave guide and m+1 branchingconnections at spaced points around the loop with a spacing of nkbetween successive branch connections, where A is the wavelength in thewave guide and n is an integer, the output of said single source beingconnected to one of said branch connections and each of said loadterminations being connected to a different one of the other m branchconnections.

3. In combination in a wave transmission system, In microwavetransmitters, a single tnansmission device and a coupling devicetherebetween for summing the outputs of said In transmitters and fordelivering the summed power to said single transmission device, saidcoupling device comprising a hybrid wave-guide ring of suitableelectrical length and m-i-l branching taps connected effectively inseries with said ring at spaced points therearound, the consecutivebranch taps around said ring being spaced from each other by n), Where Ais the wavelength within the guide and n is an integer, the outputs ofsaid m transmitters being respectively connected to a different one of mof said branch taps and the input of said transmission device beingconnected to the remaining one of said m-I-l branch taps,

References Cited in the file of this patent UNITED STATES PATENTS

